The present invention relates to a needle selection device for circular knitting machines for manufacturing socks, stockings or the like.
As is known, in knitting machines for manufacturing socks, stockings or the like there are needle selection devices which, by selecting the needles to be moved to knit at a feed of the machine, allow to produce particular patterns or designs.
In some types of circular machine said selection devices comprise multiple selectors individually arranged in one of the grooves formed in the skirt of the needle cylinder below the related needle. Said selectors can individually oscillate in the radial plane of the needle cylinder in which they are arranged from an active position, in which they protrude radially with a butt from the related groove of the needle cylinder so as to engage, by means of said butt, a selector actuation cam that moves them along their groove so as to move the overlying needle to knit, to an inactive position in which the selector is fully sunk with its butt inside its groove so that it does not engage the selector actuation cams, keeping the overlying needle in idle position, i.e. in a position in which the needle does not pick up the thread at the following feed of the machine. The oscillation of the selectors from the inactive position to the active position is performed by means of extraction cams which can be of the fixed type, i.e. fixed to the support of the needle cylinder, or of the movable type so that they can be activated or deactivated by command. Downstream of the extraction cams, along the direction of the rotation of the needle cylinder about its axis with respect to said cams, there are actuation means which perform the actual selection of the selectors according to the type of design or pattern to be produced. Some of these selection means are simply constituted by levers which laterally face the needle cylinder and are arranged at a level corresponding to the position of secondary butts of the selector. Said levers can be actuated so as to interfere with said secondary butts in order to move the selector into its inactive position, avoiding its subsequent engagement with the actuation cam, or can be moved into such a position as to not interfere with the secondary butts of the selector in order to keep the related selector in the extraction position produced by the preceding action of the extraction cams.
In some types of selection device said levers are actuated by means of electromagnetic actuators, by means of piezoelectric actuators in other types of device, and by means of pneumatic-type actuators in further types of device.
Selection devices have recently been proposed that use the different behavior of an element which acts directly or indirectly on the selector according to the magnetization to which it has been subjected. This intermediate element is magnetized by means of electromagnets which can perform a different magnetization in an extremely short time and can thus ensure diversification in selection from one needle to the next even at high needle cylinder rotation speeds.
Despite being able to achieve good precision in needle selection even at the high operating speeds of knitting machines for manufacturing socks and stockings, the selection devices proposed so far, that use the magnetization of an intermediate element acting directly or indirectly on the associated selector, have the drawback that their application requires substantial structural modifications of currently commercially available machines. Accordingly, the use of devices of this type has so far been extremely limited.
Furthermore, in many cases the application of said devices would increase the difficulty of maintenance actions performed on the machine after its assembly.